Variable and reversing hydraulic drive system for turbines

ABSTRACT

Turbine drive system including a novel hydraulic valve for providing throttling and reversing flow of hydraulic fluid through a turbine drive for a centrifuge rotor or the like. The valve may be controlled automatically by a feedback system from the centrifuge drive shaft for correcting or preventing errors in rotor speed as well as by a feedback system responsive to the pressure variations in the hydraulic supply to the turbine impeller.

United States atent Williams 1151 3,655,293 51 Apr. 11, 1972 541 VARIABLE AND REVERSING 2,886,048 5/1959 Palmenberg ..41s/17 HYDRAULIC D E TEM FOR 3,572,958 3/1971 Kure-Jensen..... ....415/l7 TURBINES 3,574,474 4/1971 Lukacs ..4l5/l7 [72] Inventor: John F. Williams, New Canaan, Conn. im ry xldrilinsrg. l lflusar tta or an um [73] Assignee: Ivan Sorvall, lnc., Newton, Conn. mey 22 Filed: Aug. 11,1970 [57] ABSTRACT Turbine drive system including a novel hydraulic valve for [21] Appl' providing throttling and reversing flow of hydraulic fluid through a turbine drive for a centrifuge rotor or the like. The

[52] U 8 Cl 415/17 valve may be controlled automatically by a feedback system 51 I .t .0 25/00 from the centrifuge drive Shaft for correcting or preventing eh n rots in rotor Speed as we" as y a feedback System responsive [58] Field Of Search ..415/l7 to the pressure variations in the hydraulic pp y to the tub bine impeller.

[56] References Cited NITED STATES PATENTS 12 l0 Drawl'ng Figures U 3,367,565 2/1968 Urban ..4l5/17 zszfl 31 33 76 926 y 11., 22 1 I #14 WA 13 4| BQQV PATENT mm 11 m2 3.655.293

SHEEIlUFtS I I 34 Q INVENTOR JOHN F. WILLIAMS BY ATTORNEY PATENTEBAPR 1 1 I872 sum 2 [1F 6 FIG. 5

INVENTOR JOHN F. WILLIAMS BY ATTO'RZEY it PATENTEDAPR 11 1912 3, 655,293

SHEET 3 BF 6 INVENTOR JOHN F. WILLIAMS PATENTEDAPR H m2 SHEET 0F 6 INVENTOR JOHN F. WILLIAMS BY PATENTEDAPR 11 1972 3,655,293

SHEET 5 BF 6 INVENTOR JOHN F. WILLIAMS ATTORNEY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to turbine drives for centrifuge rotors and the like and, more particularly, to a novel hydraulic valve for providing both throttling and reversing action for the turbine.

2. Description of the Prior Art Most of the hydraulic systems in use today use the combination of high pressure and low flow in order to provide power in the integral hp range. To obtain variable speed, common practice is to use either a variable speed motor or a variable displacement pump, or both. The oil turbine centrifuge works best with high flow and low pressure. To obtain variable output speed, it would be desirable to vary the displacement of the turbine motor. This is done in large drives by varying the pitch on the turbine blades. However, the small size of the centrifuge turbine makes a variable pitch impractical. The same result could be obtained by varying the displacement of the hydraulic pump. This is not practical because of the high noise level of present-day variable displacement hydraulic pumps. Another possibility is the use of a variable speed electric motor to drive a fixed displacement hydraulic pump, but the cost of a variable speed electric motor is excessively high at the present time.

SUMMARY OF THE INVENTION The variable speed control system herein utilizes a standard jet pump electric motor to drive a fixed displacement hydraulic pump. In one embodiment, speed is fixed at 3,600 rpm., with oil displacement at this speed being approximately 15 gallons per minute. The oil turbine drive also has a fixed displacement. In order to obtain variable speed, the present invention utilizes a novel motorized pump valve of special design. This valve proportionately throttles the 15 G.P.M. so that the turbine is supplied only the oil flow required to maintain the desired speed. The valve has been designed to provide both throttling and reversing action. By reversing the flow of oil through the turbine, the centrifuge rotor can be braked smoothly from high speed to zero rpm.

In most high pressure applications, a throttling arrangement for varying flow would be very inefficient. On the turbine drive used for an ultracentrifuge, the pressure is low and it drops off with increased throttling (as speed is reduced). This results in good efficiency over the entire speed range.

Because of the relatively low inertia of the turbine drive and the high inertia of the rotor, the hydraulic drive provides extremely accurate and smooth speed control. Feedback from the drive shaft is compared electronically with the desired set speed and an error signal actuates the motorized throttling valve to correct any error in speed. A pressure sensing transducer provides some anticipation to the error signal and helps to prevent overshoot on acceleration.

These and other novel features and advantages of the present invention will be described and defined in the following specification and claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic and diagrammatic representation of a hydraulic system for driving a turbine connected to a centrifuge rotor including in the center portion thereof a partial sectional representation of the novel hydraulic valve assembly with the valve positioned in the forward drive mode;

FIG. 2 is similar to FIG. I with the valve positioned in the reverse or braking mode;

FIG. 3 is a view taken on line 33 of FIG. 2, with the turbine impeller omitted;

FIG. 4 is a view similar to FIG. I with the valve positioned in the neutral mode;

FIG. 5 is similar to FIG. 1 with the valve positioned in the throttled mode;

FIG. 6 is an enlarged, partial vertical central section view of the valve housing, together with an elevation of the motor and linkage for controlling the valve element, the valve housing section being taken on line 6-6 of FIG. 1;

FIG. 7 is a view taken on line 77 of FIG. 6;

FIG. 8 is an exploded view of the valve assembly;

FIG. 9 is a view taken on line 9-9 of FIG. 6, and

FIG. 10 is a schematic circuit of the feedback and servo motor controls for operating the hydraulic valve.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, there are shown schematically in FIGS. 1 4, a system and apparatus in several modes of operation for controlling the speed, braking, and reversing the rotation of a turbine drive for a centrifuge or the like. The system and apparatus comprise a reservoir tank 11 defining a chamber 12 within which is mounted a suitable heat exchanger 13 or the like for controlling the temperature of the hydraulic fluid contained within said chamber.

Hydraulic fluid in chamber 12 passes through a filter 21 into a pump 22 driven by way of shaft 23 which extends through the wall of tank 11 and is connected to an electric motor 24. The output of pump 22 is connected to a pipe 25 in which a suitable relief valve 26 is connected for relieving excess pressure from the output of pump 22 and for returning excess fluid back into reservoir chamber 12. Relief valve 26 is adjusted to control the requisite pressure of hydraulic fluid passing through pipe 25 by way of port 27 to the interior of circular chamber 28 of valve housing 29 to which pressure pipe 25 is connected.

Located in a turbine housing 31 is a rotatable turbine impeller 32 to which is connected the lower end of a vertical drive shaft 33. Mounted on the upper end of shaft 33 is a centrifuge rotor 34. As shown in FIG. 3, turbine housing 31 has an inlet port 36, the inner end of which is bifurcated into two oppositely extending arcuate channels 37, each of which terminate in inwardly extending nozzles 38 which are arrayed in respect of each other. The inner ends of nozzles 38 terminate in an impeller chamber 39 within which impeller 32 rotates.

One end of a transmission pipe 40 is connected to chamber 28 by way of port 41 of valve housing 29, the other end of said transmission pipe being connected to inlet port 36 in turbine housing 31. Located in the bottom of turbine housing 31 below impeller chamber 39 is an outlet port 42 to which is connected one end of a second transmission pipe 43, the other end of which is connected by way of port 44 to chamber 28 of valve housing 29. Connected to port 46, communicating with chamber 28, is one end of a return pipe 47, the other end of which is connected to chamber 12 of reservoir tank 11.

The chamber 28 of valve housing 29 is enclosed by front plate 51 and back plate 52. See also FIGS. 6 and 8. The central portion of back plate 52 has a circular boss 53 which extends partially into chamber 28. In the regions of ports 27 and 46, which are located 180 apart from each other, boss 53 is countersunk to form triangular or otherwise suitably shaped symmetrical recesses 54 and 55, which communicate with ports 27 and 46, respectively. Front plate 51 has a circular boss 56 which extends partially into chamber 28. Located within valve chamber 28 is a rotatable valve element, generally designated 57, comprising an axial shaft 58 having integrally formed vanes 61 and 62 which extend 180 apart in opposite directions. The overall end-to-end aggregate length of vanes 61 and 62 is substantially equal to the interior diameter of chamber 28, while the ends of said vanes are provided with arcuate surfaces which form a sliding contact with the inner circular wall of chamber 28 whereby said vanes diametrically divide said chamber into two substantially equal subchambers. The front and rear edges of vanes 61 and 62 form a close sliding fit with the inner surfaces of bosses 53 and 56 whereby leakage of hydraulic fluid between the two subchambers formed by valve element 57 is substantially prevented.

The opposite ends of shaft 58 are supported in needle bearings 63 and 64 located in suitable recesses in back plate 52 and front plate 51, respectively. Plates 51 and 52 are secured to circular valve housing 29 by means of a plurality of spaced apart screws 66 with O-rings 67 and 68 located in suitable annular recesses ensuring against leakage between said component parts. One end of shaft 58 extends through front plate 51 to the exterior of the valve housing for connection to other component parts of the system which will be explained hereinafter. A suitable O-ring 69 is provided in plate 51 for preventing leakage around that portion of the shaft 58 which extends through plate 51.

Back plate 52 also serves as a mounting plate whereby the valve assembly may be secured to a suitable platform, stand, or associated apparatus by means of bolts 70, or the like, with an O-ring 71 in a suitable recess for preventing leakage of hydraulic fluid.

FIG. 6 shows an integrally formed, outwardly extending bushing 72 which serves as a coupling means between pressure pipe 25 and port 27 in back plate 52 with O-ring 73 providing a liquid-tight seal.

The basic operating action of the valve herein is the division of the valve housing chamber 28 by the diametric valve 57 into a pressure chamber and a return chamber, said pressure chamber being established by communication between port 27 and port 41, while the return flow chamber is established by communication between port 44 and port 47. Variation in the hydraulic pressure transmitted through port 41 and pipe 40 is determined by the extent to which the flow of hydraulic fluid is varied by the relationship of vanes 61 of valve 57 to port 27.

Manifestly, by bypassing some of the hydraulic fluid from port 27 directly to port 46, a proportionately lesser amount of hydraulic fluid will be transmitted through port 41 and pipe 40 to the turbine impeller 32. Simultaneous action of vanes 61 and 62 relative to ports 27 and 46, respectively, control the throttling action.

Although an operable valve device may be made with the mouths of ports 27 and 46 terminating at the inner surface of boss 53 of plate 52, a finer degree of control is achieved by including the respective countersunk recesses 54 and 55, whose contours are symmetrically arrayed on both sides of the respective ports and which effectively enlarge the mouths thereof. Therefore, despite the limited diameter of ports 27 and 46, the extent of the circular motion of valve vanes 61 and 62 relative to said ports is considerably increased by virtue of said countersunk recesses so that there is a greater ratio of movement of the valve relative to the size of said ports.

When valve 57 is located in a position where its vanes 61 and 62 are in a horizontal array as in FIG. 1, and where they divide chamber 28 into separate subcompartments, all of the hydraulic fluid entering under pressure into the high pressure subcompartment by way of port 27 is transmitted through pipe 40, through channels 37 and noules 38, to drive turbine impeller 32, whereby the full force of the hydraulic pressure is directed to turning centrifuge rotor 34. All of the spent hydraulic fluid passing through port 42 and pipe 43 enters into the return subcompartment of chamber 28 and returns through port 46 and pipe 47 to chamber 12 of reservoir tank 11. As represented in FIG. 1, the system operates as a full speed forward mode wherein the total hydraulic energy is directed to turning centrifuge rotor 34.

When it is desired to use the hydraulic system as a brake to decelerate the centrifuge to a smooth stop, valve element 57 is rotated 90 counterclockwise to a vertical position as shown in FIG. 2. With the valve element 57 in this position, the force of the hydraulic fluid entering from pipe 25 into chamber 28 is directed through port 44 and through pipe 43 and through port 42 of turbine housing 31, whereby the force of the hydraulic fluid is exerted on the rear faces of the turbine impeller vanes thereby causing said impeller to decelerate and ultimately to come to a stop at which time the pump motor 24 would be stopped. If valve element 57 continues to be maintained in its vertical position as shown in FIG. 2, and motor 24 continues to run, then the continuing impingement of the hydraulic fluid on the reverse surfaces of the turbine impeller blades will thereafter cause said impeller to rotate in the reverse or opposite direction if such action is necessary or desired.

By positioning the valve element 57 at approximately a 45 angle in the neutral mode, as illustrated in FIG. 4, vanes 61 and 62 are arrayed diagonally so that they are located directly or centrally over ports 27 and 46, respectively. In this position, the stream of hydraulic fluid in pipe 25 entering port 27 is then divided into two branches flowing to respective opposite sides of vane 61 by way of countersunk recess 54. Vane 62 also substantially bisects outlet port 46 whereby fluid passes into said port from both sides of valve element 57 by way of countersunk recess 55. In this position, system pressure is reduced to practically zero.

In many operating conditions, after the centrifuge is brought up to a desired speed in the forward mode conditions as illustrated in FIG. 1, the effect of the full hydraulic force is no longer necessary since comparatively little energy is required to maintain the centrifuge at the desired speed. By making minute adjustments to the angularity of valve element 57 in relation to ports 27 and 46, it is possible to establish the requisite relative hydraulic pressure on the respective op posite sides of said valve element to produce sufficient fluid force passing through pipe 40 to maintain the rotation of centrifuge rotor 34 at a requisite or desired speed. Accordingly, hydraulic fluid under pressure entering into chamber 28 by way of port 27 is only partially directed into pipe 40 for driving impeller 32 while the remainder of said fluid passes out through exit port 46 into reservoir tank 11. Spent hydraulic fluid emerging from turbine port 42 and passing through pipe 43 also passes through chamber 23 and is transmitted through port 46 and pipe 47 into reservoir tank 11.

The complete variability of control for regulating the speed of the centrifuge is shown in FIG. 5 which illustrates the throttling mode of the control valve herein. By positioning valve element 57 at somewhat less than a 45 angle from the horizontal, it will be seen that by permitting a greater amount of the hydraulic force to be transmitted from inlet port 27 to outlet port 41, the speed of the centrifuge rotor 34 is thereby increased as compared with the speed established in the neutral mode as shown in FIG. 4. When it is desired to reduce the speed of the turbine drive, valve element 57 may be rotated to a position somewhat greater than 45 from the horizontal, as shown in dotted outline in FIG. 5, whereby less hydraulic power is transmitted through pipe 40 to turbine impeller 32. It is evident that infinite variability of speed of centrifuge rotor 34 may be achieved according as the angle of valve 57 is varied in its positions relative to countersunk recesses 54 and 55, as indicated schematically in FIG. 5.

In all of the foregoing description of the operating modes in FIGS. 1, 2, 4 and 5, it is possible to operate valve element 57 to assume the various control positions by means of a manually operated handle, crank, or the like, connected to shaft 58 located externally of the valve housing. It is also advantageous to provide for automatic means to control the speed of the centrifuge whereby a suitable sensing and feedback system can be incorporated for producing automatic speed control action, as will be described hereinafter.

Because of the relatively low inertia of the turbine drive as represented by impeller 32 and the high inertia of centrifuge rotor 34, the hydraulic drive system is conducive to extremely accurate and smooth speed control as may be required or desired. Automatic control of the system is achieved by incorporating therein a sensor 76, selected from a number of devices well known in the art, which measures the rotation of speed of the rotor by magnetic, optical, or other means, the information of which is transmitted by a suitable electronic transmission circuit 77 to an electronic speed comparator 78. The comparator instrument 78 comprises a dial 79 that is marked in suitable graduations, as for example, thousands rpm. Movable across dial 79 is a set point needle 81 which is positioned at the desired speed at which the centrifuge is to rotate, said needle being manually operated by set knob 82. The actual running speed of rotor 34 as transmitted by sensor 76 and circuit 77 is indicated on dial 79 by speed read-out needle 83. Comparator 78 has an error detector circuit which calculates the difference between the set point needle 81 and speed read-out needle 83, and transmits said error detection or speed differential, whether positive or negative, to a servo motor 84 which, by way of gear reducing device 86 and coupling element 87, is connected to outwardly extending spindle 91 integrally formed on shaft 58 of valve 57. See also FIG. 6.

Also mounted on spindle 91 is a valve cam 92 secured thereon by means of spring pin 93 extending through said cam and said spindle. See FIGS. 6 and 8. Mounted on the outer surface of front plate 51 in a generally circular array surrounding spindle 91 are four microswitches A, B, C and D, having bearing rollers 94, 96, 97 and 98 on their respective actuator levers which are engaged by the outer edge of cam 92 at difierence predetermined times depending upon the rotation of valve 57.

The camming contour of cam 92 is suitably formed in accordance with the conditions of the valve and of the particular location of roller bearing elements 94, 96, 97 and 98. Microswitch A operates as a reverse neutral switch; microswitch B operates as a forward neutral switch; microswitch C operates as a forward limiting switch; and microswitch D operates as a reverse limiting switch. Said cam contour and the locations of said roller bearing elements are a matter of choice, design, and convenience in relation to the assembly and operation of the apparatus herein.

Another variable factor taken into account in the operation of the apparatus herein is the fluid pressure prevaling in pipe 40. Accordingly, a suitable pressure sensor transducer E, known in the art, is connected in pipe 40 to monitor the pressure prevailing in that pipe, and to transmit continuously a suitable electrical signal that varies proportionately as said pressure varies.

The information that is received from the comparator or error detector 78 from microswitches A, B, C and D, and from pressure sensor E, is fed into a control logic circuit F, as shown graphically in FIG. 1, and in schematic circuit form in FIG. 10. Sensor 76 may comprise a commercially available magnetic pickup, the pulsed signal of which is fed into a basic balanced amplifier circuit which, in turn, is connected to a Magmeter, manufactured by Airpax Electronics, which improves the pulse shape received from the amplifier. The improved pulse signal is next transmitted through a rectifier which converts the pulses to a dc. signal proportionate to the frequency of rotation of rotor 34. The amplifier, Magmeter, and rectifier are represented by circuit box 77 in FIG. 1. Error detector 78 is a commercially available tachometer device as exemplified by Model MR-24-06-01, manufactured by Beede Electrical Instruments, Inc.

Control logic F contains a bridge circuit which receives information from speed sensor 76 and from turbine input pressure sensor E, and integrates that information in a resultant signal transmitted either to the logic forward circuit or to the logic reverse circuit which control a respective forward drive circuit or a reverse drive circuit, both of which are connected to gear motor 84. Said gear motor is a commercially available product which is exemplified by Model B215 OE-36, manufactured by Bodine Motors, Inc. The signal from the forward drive circuit or from the reverse drive circuit causes gear motor 84 to rotate valve 57 in a corresponding forward or reverse motion to the appropriate position within valve housing 29 to modify the pressure of the fluid delivered to impeller 32 for either accelerating or decelerating the latter. Microswitches A and D are connected to the reverse drive circuit, while microswitches B and C are connected to the forward drive circuit, whereby the rotation of valve 57 is directionally controlled and limited.

By the foregoing means, or suitable modifications thereof, complete automatic operation of speed control for a centrifuge rotor is achieved with the hydraulic valve being responsive to a plurality of variable conditions so that the desired or requisite acceleration, speed, and deceleration of the centrifuge rotor is achieved, as well as the corrections of transient deviations from the desired speed of the impeller. By virtue of the integrating circuitry described hereinbefore, the single valve element herein is rendered capable of transmitting the required amount of fluid to the positive side of impeller 32 for any required or desired degree of forward speed, or to the negative side of said impeller for any required or desired degree of reverse or braking speed within the capacities of the component parts of the system.

Limiting microswitches C and D prevent said valve from rotating beyond limits in either direction while forward and reverse neutral switches A and B transmit information to the integrating circuit as to the particular location of the valve during each moment in time so that said circuit can, in turn, produce the necessary correcting or instructed action required for the operation of the turbine impeller as to acceleration, deceleration, and speed maintenance.

Although the present invention has been described with reference to particular embodiments and examples, it will be apparent to those skilled in the art that variations and modifications can be substituted therefor without departing from the principles and true spirit of the invention. The Abstract given above is for the convenience of technical searchers and is not to be used tor interpreting the scope of the invention or claims.

lclaim:

1. Hydraulic control system for a turbine drive or the like, comprising a source of hydraulic fluid under pressure, a turbine impeller, a valve assembly connected between said source and said impeller, first means for transmitting fluid under pressure to said valve, second means for transmitting fluid under pressure from said valve assembly to said impeller, third means for returning spent fluid from said impeller to said valve assembly, fourth means for returning spent fluid from said valve assembly to said source, and a rotatable valve in said valve assembly, said valve being movable relative to said four means between the two opposite extremes of causing (a) full pressure delivery of hydraulic fluid to said impeller; (b) reverse flow of fluid to decelerate and stop the rotation of said impeller; and (c) gradations of pressure delivery to said impeller between said two extremes of (a) and (b).

2. Hydraulic control system for a turbine drive or the like comprising a source of hydraulic fluid under pressure, a turbine impeller, a valve assembly connected between said source and said impeller, first means for transmitting fluid under pressure to said valve, second means for transmitting fluid under pressure from said valve assembly to said impeller, third means for returning spent fluid from said impeller to said valve assembly, fourth means for returning spent fluid from said valve assembly to said source, and a valve rotatable in said valve assembly into selected positions where: (a) said first and second means are isolated from said third and fourth means for full forward drive of said impeller; (b) said first and third means are isolated from said second and fourth means for full reverse drive of said impeller; and (c) in locations between those described in (a) and (b) various gradations of impeller speed are produced between full forward and full reverse drive of said impeller.

3. Hydraulic control system for a turbine drive or the like comprising a source of hydraulic fluid under pressure, a turbine impeller, a valve assembly connected between said source and said impeller, first means for transmitting fluid under pressure to said valve, second means for transmitting fluid under pressure from said valve assembly to said impeller, third means for returning spent fluid from said impeller to said valve assembly, and fourth means for returning spent fluid from said valve assembly to said source, said valve assembly comprising a valve body, a circular chamber in said body, a first end plate and a second end plate enclosing said chamber, a diametrical valve rotatably mounted within said chamber,

said valve forming a sliding fit with the inner circumference of said chamber and with said end plates, and a pair of first and second ports in said first end plate and arrayed 180 apart from each other, said first port being connected to said first means, said second port being connected to said fourth means.

4. A system according to claim 3 and further comprising a countersunk recess surrounding each of said ports in said end plate for effectively enlarging respective mouths thereof across which said valve moves.

5. A system according to claim 3 and further comprising third and fourth ports located diametrically opposite each other in said valve housing, said third port being connected to said second means and said fourth port being connected to said third means.

6. A hydraulic control system for a turbine drive or the like comprising a source of hydraulic fluid under pressure, a turbine impeller, said impeller having a positive side for forward drive and a negative side for reverse or braking drive, a valve assembly connected between said source and said impeller, first means for transmitting fluid under pressure from said source to said valve, second fluid connecting means between said valve assembly and the positive side of said impeller, third fluid connecting means between the negative side of said impeller and said valve assembly, fourth means for returning fluid from said valve assembly to said source, a valve in said valve assembly, said valve being positionable to transmit hydraulic fluid under pressure selectively to either the positive side or the negative side of the impeller, said valve being movable into a plurality of positions for varying the pressure of hydraulic fluid transmitted to said impeller, a gear motor connected to said valve, means for sensing the rotational speed of said impeller and integrating means connected between said sensing means and said gear motor for causing said motor to adjust the position of said valve.

7. A system according to claim 6 and further comprising pressure sensing means connected between said second fluid connecting means and said integrating means for monitoring the pressure in said second means and for causing said valve to accommodate to variations in pressure in said second means.

8. A system according to claim 6 and further comprising speed setting means connected to said integrating means, and error correcting means between said sensing means and said speed setting means for correcting transient deviations from a desired speed of said impeller.

9. A system according to claim 8 and further comprising switch means connected between said valve and said integrating means for limiting the rotation of said valve between the settings for full forward and full reverse drive of said impeller.

10. A system according to claim 9 and further comprising second switch means connected between said valve and said integrating means for indicating and transmitting information to said integrating means as to the location of said valve in either the forward, neutral, and reverse modes.

11. A hydraulic control system comprising a source of hydraulic fluid under pressure, a hydraulically driven load capable of forward and reverse motion, a valve assembly connected between said source and to the fluid input and fluid output of said load, said valve assembly including a rotatable valve therein, said valve being movable between two opposite extremes for causing (a) full pressure delivery of hydraulic fluid to the fluid input of said load for forward motion thereof; (b) reverse flow of fluid delivered to the fluid output of said load to decelerate and stop the motion thereof; and (c) gradations of pressure delivery selectively to either said input and output between the two extremes of (a) and (b).

12. A system according to claim 11 wherein said valve assembly comprises a valve body, a circular chamber in said body, a first end plate and a second end plate enclosing said chamber, a diametrical valve rotatably mounted within said chamber and forming a sliding fit with the inner circumference of said chamber and with said end plates, a pair of spaced first and second diametrically arrayed ports in said first end plate, said first port bein connected to said source, said second port transmitting spen fluid to said source, and spaced third and fourth diametrically arrayed ports extending through the circular wall of said valve body, said third p011 being connected to the fluid input of said load and said fourth port being connected to the fluid output of said load. 

1. Hydraulic control system for a turbine drive or the like, comprising a source of hydraulic fluid under pressure, a turbine impeller, a valve assembly connected between said source and said impeller, first means for transmitting fluid under pressure to said valve, second means for transmitting fluid under pressure from said valve assembly to said impeller, third means for returning spent fluid from said impeller to said valve assembly, fourth means for returning spent fluid from said valve assembly to said source, and a rotatable valve in said valve assembly, said valve being movable relative to said four means between the two opposite extremes of causing (a) full pressure delivery of hydraulic fluid to said impeller; (b) reverse flow of fluid to decelerate and stop the rotation of said impeller; and (c) gradations of pressure delivery to said impeller between said two extremes of (a) and (b).
 2. Hydraulic control system for a turbine drive or the like comprising a source of hydraulic fluid under pressure, a turbine impeller, a valve assembly connected between said source and said impeller, first means for transmitting fluid under pressure to said valve, second means for transmitting fluid under pressure from said valve assembly to said impeller, third means for returning spent fluid from said impeller to said valve assembly, fourth means for returning spent fluid from said valve assembly to said source, and a valve rotatable in said valve assembly into selected positions where: (a) said first and second means are isolated from said third and fourth means for full forward drive of said impeller; (b) said first and third means are isolated from said second and fourth means for full reverse drive of said impeller; and (c) in locations between those described in (a) and (b) various gradations of impeller speed are produced between full forward and full reverse drive of said impeller.
 3. Hydraulic control system for a turbine drive or the like comprising a source of hydraulic fluid under pressure, a turbine impeller, a valve assembly connected between said source and said impeller, first means for transmitting fluid under pressure to said valve, second means for transmitting fluid under pressure from said valve assembly to said impeller, third means for returning spent fluid from said impeller to said valve assembly, and fourth means for returning spent fluid from said valve assembly to said source, said valve assembly comprising a valve body, a circular chamber in said body, a first end plate and a second end plate enclosing said chamber, a diametrical valve rotatably mounted within said chamber, said valve forming a sliding fit with the inner circumference of said chamber and with said end plates, and a pair of first and second ports in said first end plate and arrayed 180* apart from each other, said first port being connected to said first means, said second port being connected to said fourth means.
 4. A system according to claim 3 and further comprising a countersunk recess surrounding each of said ports in said end plate for effectively enlarging respective mouths thereof across which said valve moves.
 5. A system according to claim 3 and further comprising third and fourth ports located diametrically opposite each other in said valve housing, said third port being connected to said second means and said fourth port being connected to said third means.
 6. A hydraulic control system for a turbine drive or the like comprising a source of hydraulic fluid under pressure, a turbine impeller, said impeller having a positive side for forward drive and a negative side for reverse or braking drive, a valve assembly connected between said source and said impeller, first means for transmitting fluid under pressure from said source to said valve, second fluid connecting means between said valve assembly and the positive side of said impeller, third fluid connecting means between the negative side of said impeller and said valve assembly, fourth means for returning fluid from said valve assembly to said source, a valve in said valve assembly, said valve being positionable to transmit hydraulic fluid under pressure selectively to either the positive side or the negative side of the impeller, said valve being movable into a plurality of positions for varying the pressure of hydraulic fluid transmitted to said impeller, a gear motor connected to said valve, means for sensing the rotational speed of said impeller and integrating means conneCted between said sensing means and said gear motor for causing said motor to adjust the position of said valve.
 7. A system according to claim 6 and further comprising pressure sensing means connected between said second fluid connecting means and said integrating means for monitoring the pressure in said second means and for causing said valve to accommodate to variations in pressure in said second means.
 8. A system according to claim 6 and further comprising speed setting means connected to said integrating means, and error correcting means between said sensing means and said speed setting means for correcting transient deviations from a desired speed of said impeller.
 9. A system according to claim 8 and further comprising switch means connected between said valve and said integrating means for limiting the rotation of said valve between the settings for full forward and full reverse drive of said impeller.
 10. A system according to claim 9 and further comprising second switch means connected between said valve and said integrating means for indicating and transmitting information to said integrating means as to the location of said valve in either the forward, neutral, and reverse modes.
 11. A hydraulic control system comprising a source of hydraulic fluid under pressure, a hydraulically driven load capable of forward and reverse motion, a valve assembly connected between said source and to the fluid input and fluid output of said load, said valve assembly including a rotatable valve therein, said valve being movable between two opposite extremes for causing (a) full pressure delivery of hydraulic fluid to the fluid input of said load for forward motion thereof; (b) reverse flow of fluid delivered to the fluid output of said load to decelerate and stop the motion thereof; and (c) gradations of pressure delivery selectively to either said input and output between the two extremes of (a) and (b).
 12. A system according to claim 11 wherein said valve assembly comprises a valve body, a circular chamber in said body, a first end plate and a second end plate enclosing said chamber, a diametrical valve rotatably mounted within said chamber and forming a sliding fit with the inner circumference of said chamber and with said end plates, a pair of spaced first and second diametrically arrayed ports in said first end plate, said first port being connected to said source, said second port transmitting spent fluid to said source, and spaced third and fourth diametrically arrayed ports extending through the circular wall of said valve body, said third port being connected to the fluid input of said load and said fourth port being connected to the fluid output of said load. 